Techniques of Water Resources Investigations publication, "Finite-difference model for aquifer simulation in two dimensions with results of numerical experiments," UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY RESTON, VIRGINIA 22092 GW Branch August 27, 1976 Code 4351 5016 GROUND WATER BRANCH TECHNICAL MEMORANDUM NO. 76.12-T Subject: PUBLICATIONS - Techniques of Water Resources Investigations publication, "Finite- difference model for aquifer simulation in two dimensions with results of numerical experiments," Book 7, Chapter C1, by P. C. Trescott, G. F. Pinder, and S. P. Larson. The attached techniques manual by Peter Trescott, George Pinder, and Steve Larson supersedes the techniques manual published in 1970 entitled, "A digital model for aquifer evaluation," by George F. Pinder as Chapter C1 of Book 7. The new Chapter C1 represents a significant improvement in the computation capability to solve the flow equations and has greater flexibility in the hydrologic situations that can be simulated. The model will simulate ground-water flow in an artesian aquifer, a water-table aquifer, a combined artesian and water-table aquifer, or an aquifer that changes from artesian to water-table conditions, or vice versa. It may also simulate certain types of cross sectional flow problems. The aquifer may be heterogeneous and anisotropic and have irregular boundaries. The source term in the flow equation accommodates multiple pumping periods, recharge, leakage from confining beds in which the effects of storage are considered, and evapotranspiration from a water-table aquifer as a linear function of depth to water. The model allows the user to select an equation-solving scheme from among the iterative alternating-direction implicit procedure (IADIP), line successive overrelaxation (LSOR), and the strongly implicit procedure (SIP). Results of numerical experiments are provided to give some insight as to the numerical scheme that may be preferable for a given flow problem. (s) Charles A. Appel for Chief, Ground Water Branch Water Resources Division Attachment WRD Distribution: A, B, S, FO, PO